Data traffic in mobile telecommunications networks is continually increasing. Consequently, operators are employing heterogeneous access networks that utilise multiple radio access technologies (RATs) in order to provide greater capacity, particularly in high traffic areas and areas that otherwise have poor network coverage.
Typically, the radio access technologies utilised as part of these heterogeneous access networks include UMTS Radio Access Network (UTRAN) and an Evolved UTRAN (eUTRAN), and Wi-Fi/WLAN RAN. For example, FIG. 1 illustrates schematically a heterogeneous access network comprised of a UTRAN, an eUTRAN, and a Wi-Fi/WLAN RAN. In this regard, both the UTRAN and eUTRAN standards are defined by the 3rd Generation Partnership Project (3GPP), and the relevant 3GPP standards therefore define capabilities for interaction between these 3GPP RANs. In contrast, the Wi-Fi/WLAN standards are defined by the Institute of Electrical and Electronics Engineers (IEEE), and neither the IEEE standards nor the 3GPP standards define capabilities for interaction between a Wi-Fi/WLAN network and a 3GPP network. Furthermore, as a WLAN network and a 3GPP network are part of separate domains that use different management systems, different paradigms, different identities etc., there is no mechanism that allows either network to determine information relating to the other network.
Consequently, for a device/user terminal (i.e. user equipment (UE), station (STA) etc) that is both 3GPP and WiFi/WLAN capable, and can therefore move between a 3GPP network and a WLAN, the decision to move between a 3GPP network and a WLAN will be made by the user terminal. For example, for most currently available user terminals, when the user terminal is within the coverage of both a WLAN and a 3GPP network, the user terminal will automatically attempt to connect to the WLAN and will detach from the 3GPP network. As a further example, a user terminal could decide to attempt to associate with a WLAN if the connection to a 3GPP network is poor. In such circumstances, neither the 3GPP network nor the WLAN will have any knowledge of each other, and it will therefore appear to the serving/source network (i.e. the network from which the user terminal is moving) as if the user terminal is merely disconnecting, whilst the user terminal has in fact moved to an alternative network.
It has been recognised here that one issue that arises from the fact that movement between a WLAN and a 3GPP network is determined by the user terminal, and the lack of knowledge within the networks regarding such movement, is that it is then very difficult to troubleshoot any problems, faults or errors that occur. For example, consider a scenario in which a user terminal is using a connection to a 3GPP network to obtain a streamed video when the user terminal then decides to move to a WLAN, yet subsequently receives poor performance from the WLAN that causes the video to freeze frequently. If the user of the user terminal contacts customer care of their mobile operator regarding this issue, the mobile operator will only be able to determine that the user terminal disconnected from the 3GPP network and will not be able to ascertain any further information in order to determine the actual cause of the issue. In particular, the mobile operator will have no knowledge that the issue was caused by a move to another network that resulted in a change in the radio access technology.
In addition, due to the increasing availability of heterogeneous radio access networks, mechanisms for providing access selection and traffic steering between the different radio access technologies is being considered. When this functionality becomes available, the ability to observe the movement of user terminals between the radio access technologies will then be particularly important, e.g. in order to determine the effect of configuration changes.